1. Field of the Invention
The present invention relates to a communication terminal device connected to a communication network via information channels used for transmission of line switching information, packet switching information or the like and a signal channel used for control of a call to an objective communication terminal, and more particularly to a communication terminal device which performs efficient communication processings using the information channels effectively in a communication network in which at least two channels are disposed as the information channels.
2. Description of the Prior Art
An information channel for transfer of switching information and a signal channel for transfer of control information may be separated in a communication network such that control information can be transmitted, for example, via the signal channel separately, at any time from voice information or image information as switching information, or such that a plurality of information channels can be controlled via a single signal channel to provide various services different in nature such as telephone, telex or facsmile synthetically and efficiently. One such network is known conventionally as ISDN (Integrated Services Digital Network).
In ISDN, the information channels and the signal channels are called B- and D-channels, respectively. Especially in the D-channel, identification information on a caller's communication terminal is transmitted additionally as the control information. Therefore, in the called communication terminal, it can be known, in accordance with the identification information on the caller's communication terminal transmitted via the D-channel, which of the communication terminals has transmitted the information (voice information and image information) in the B-channel.
In ISDN, a plurality of channels is provided as information channels (B-channels) in order to controllably handle various services different in nature such as telephone, telex and facsimile. Thus, the transmission of information is possible in the form of simultaneous transmission of voice information and image information using two empty information channels.
More specifically, if there is an incoming telephone call in a first information channel during communication of image information in a G4 facsimile mode in a second information channel, simultaneous communication of image and voice is selected to continue the operation between the appropriate communication terminal device.
According to such ISDN, it is true that the above various services can be realized synthetically and efficiently, and also simultaneous communication of image and voice is possible, as mentioned above, but, for example, the existing facsimile device connected to the ISDN is limited in use to the communication of image information in the G4 facsimile mode and voice information on regular telephone communication although simultaneous communication of image and voice is possible, so that the efficient use of the whole communication network is not necessarily achieved.
For example, the following requirements are essential for realizing a very significant form of use in order to improve the user interface as the communication terminal device or in order to improve the communication efficiency of the whole communication network:
(a) When there is an originating telephone call in the second information channel during the communication of image information in the G4 facsimile mode in the first information channel, the originating telephone call relating to a request for receipt of image information in the G3 facsimile mode, the call should be received;
(b) When there is an originating telephone call in the second information channel during telephone communication in the first information channel, the originating telephone call relating to a request for receipt of image information in the G3 facsimile mode, the call should be received;
(c) When there is an originating telephone call in the second information channel during telephone communication in the first information channel, the call relating to a request for telephone communication, the call should be received; and
(d) When there is an originating telephone call in the second information channel during telephone communication in the first information channel, the call relating to a request for telephone communication, the call should be recorded by an automatic answering system.
However, some existing communication terminal devices cannot virtually realize these requirements in whatever manner they are connected to the ISDN.